The “cellulase” is a collective name denoting the enzyme group that catalyzes an enzyme reaction system in which cellulose is hydrolyzed into glucose, cellobiose, or cellooligotose. Depending on the catalytic mechanism, there are enzymes referred to as FPase, CMCase, cellobiase, and the like. Cellulase degrades cellulose into glucose as an end product of degradation via interaction among such enzymes.
The “hemicellulase” is a collective name denoting the enzyme group that catalyzes an enzyme reaction system in which hemicellulose is hydrolyzed into xylose, arabinose, mannose, galactose, or the like. Depending on the catalytic mechanism, there are enzymes referred to as xylanase, arabinanase, arabinofuranosidase, mannanase, galactanase, xylosidase, mannosidase, and the like.
Hitherto, microorganisms such as Trichoderma reesei (Biotechnol. Bioeng., 23, 1837-1849 (1981)), Trichoderma viride (T. viride) (Appl. Biochem. Biotechnol., 57-58, 349-360 (1996)), and microorganisms belonging to the genera Aspergillus, Penicillium, and the like, have been used as cellulase-producing fungi for producing cellulase and/or hemicellulase, which can be used for saccharification of lignocellulose biomass. However, by use of such microorganisms, satisfied productivity of cellulase was not able to be achieved, which was a drawback. In addition, the produced cellulase did not have a sufficient ability to degrade cellulose, meaning that the known cellulose enzymes cannot completely degrade cellulose into glucose. Accordingly, there is a problem that a large amount of cellobiose and cellooligosaccharide, which are intermediates, are produced and remains during the degradation of cellulose.
To solve the above-mentioned problems, it has been attempted to intensively isolate from the nature, microorganisms which have a high ability to produce cellulase and an ability to produce cellulase having high activity. As a result, a microorganism belonging to Acremonium cellulolyticus, which can substantially completely degrade cellulose into glucose, was isolated from soil by us (JP 59-166081 A (1984)). We have further found that the mutant Acremonium cellulolyticus C1 strain (FERM P-18508) had a higher ability to produce cellulase when compared with said parent microorganism (JP 2003-135052 A).
In recent years, there has been a great interest in that biomass is subjected to enzymatic degradation and saccharification using cellulase and/or hemicellulase to convert it into constituent units like glucose, xylose, arabinose, mannose, and galactose, which are used to produce fermentation products such as ethanol and lactic acid that can be utilized as a liquid fuel or chemicals. Thus, the development of a technology for practical application of biomass has been carried out actively. Hence, for the purpose of an economical and practical use of biomass, there is a great demand on microorganisms with an ability to produce cellulase more highly than the known cellulase-producing fungi as described above.
Under the above-described circumstances, it is an objective of the present invention to efficiently produce cellulase and/or hemicellulase and to efficiently degrade or saccharify biomass, through improving the ability to produce cellulose in cellulase-producing microorganisms.